The word(s) "ولكني" appears in 4 verse(s) in Quran.

(1) قَالَ يَا قَوْمِ لَيْسَ بِي ضَلَالَةٌ وَلَـٰكِنِّي رَسُولٌ مِّن رَّبِّ الْعَالَمِينَ

(سورة الأعراف, Al-A'raaf, Chapter #7, Verse #61)
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(2) قَالَ يَا قَوْمِ لَيْسَ بِي سَفَاهَةٌ وَلَـٰكِنِّي رَسُولٌ مِّن رَّبِّ الْعَالَمِينَ

(سورة الأعراف, Al-A'raaf, Chapter #7, Verse #67)
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(3) وَيَا قَوْمِ لَا أَسْأَلُكُمْ عَلَيْهِ مَالًا ۖ إِنْ أَجْرِيَ إِلَّا عَلَى اللَّهِ ۚ وَمَا أَنَا بِطَارِدِ الَّذِينَ آمَنُوا ۚ إِنَّهُم مُّلَاقُو رَبِّهِمْ وَلَـٰكِنِّي أَرَاكُمْ قَوْمًا تَجْهَلُونَ

(سورة هود, Hud, Chapter #11, Verse #29)
(Arabic, Transliteration, Urdu (Ahmed Ali), Urdu (Jalandhry), Farsi, Yusuf Ali, Shakir, Picthal, Mohsin Khan, French, Spanish, Indonesian, Malay, German, Bosnian, Russian, Dutch, Italian, Portuguese, Tafsir - Jalal ad-Din, Tafsir - King Fahad Quran Complex)

(4) قَالَ إِنَّمَا الْعِلْمُ عِندَ اللَّهِ وَأُبَلِّغُكُم مَّا أُرْسِلْتُ بِهِ وَلَـٰكِنِّي أَرَاكُمْ قَوْمًا تَجْهَلُونَ

(سورة الأحقاف, Al-Ahqaf, Chapter #46, Verse #23)
(Arabic, Transliteration, Urdu (Ahmed Ali), Urdu (Jalandhry), Farsi, Yusuf Ali, Shakir, Picthal, Mohsin Khan, French, Spanish, Indonesian, Malay, German, Bosnian, Russian, Dutch, Italian, Portuguese, Tafsir - Jalal ad-Din, Tafsir - King Fahad Quran Complex)